Meisn., Linnaea 11:194.1837
M. pachyphyllum Pitt.
Liana or arching and scandent tree, to ca 15 m tall; trunk to ca 12 cm diam, the upper part straight, rarely branched, usually arching or pendent from trees; old stems armed with recurved, spiny, woody stipules and conspicuous, stiff, long setae. Leaves compound, clustered near stem apex; stipules triangular, to 2 cm long and 1 cm wide, pubescent, paired, becoming woody in age; petioles to 8 cm long, the pulvinus conspicuous, terete, sparsely pubescent; petiolules stout, ca 5 mm long; leaflets 11-17, mostly oblong, long-acuminate, rounded to truncate or obtuse at base, 4-17 cm long, 2-6 cm wide, usually glabrous or reddish-villous on midrib below, coriaceous, the reticulate veins prominulous, about as conspicuous as the major lateral veins, the margins conspicuously enlarged and discolored. Panicles axillary or terminal, to 90 cm long, usually less than 50 cm long, on short, lateral, usually leafy branches on the terminal 3-4 m of the stem; rachises, peduncles, pedicels, and calyces bearing dense velvety-brown pubescence; flowers to 1.5 cm long; calyx subtended by 2 ovate bracts appressed to the anterior lobes, the carinal tooth acute, exceeding lateral lobes; standard spreading, rufous-pubescent outside, glabrous and lavender inside at least near apex, the center greenish, fringed with violet-purple; wings and keel usually white, weakly held together, the keel petals fused along their outer margin; free stamen united to the staminal tube, all stamens ± equal, the apical fourth free, strongly turned inward, the free part alternating with short erect appendages; style exceeding the anthers; pistil densely appressed-pilose. Samaras oblong, ca 8 cm long and 2 cm wide, distally winged; seminiferous area narrower, ca 2 cm long, rufous-villous, the trichomes interspersed with much stouter trichomes that have dark swollen bases. Croat 5346, 13984.
Occasional, in the forest and along the shore. Flowering infrequently, usually in the early dry season (February and March). Immature fruits have been seen in early April; fruits probably mature in April and May. Leaves are deciduous just before flowering.
Easily distinguished by its larger inflorescences and flowers and by the conspicuous setae on the stems.
This species was reported by Standley (1933) and by Johnston (1949) as M. marginatum Standl. Although the paratype of that species is referable to M. kegelii, the holotype of M. marginatum is referable to M. microphyllum.
The pollinator is apparently a strong bee, since the flower is strong and the keel is not easily moved.
Costa Rica and Panama. In Panama, known from tropical moist forest in the Canal Zone (both slopes) and Panama (San Jose Island), from tropical dry forest in Coclé (Penonomé), and premontane moist forest in Panama (Panama City).
See Figs. 289 and 290.